Muck On River Bottom To Tell A Tale Of Navy

August 29, 1995|By RICHARD STRADLING Daily Press

GLOUCESTER — She's into worms. He's into mud. Together they're trying to figure out how pollution moves across the bottoms of rivers and bays.

Biologist Linda Schaffner and geologist Don Wright are scientists at the Virginia Institute of Marine Science at Gloucester Point. They watched from the deck of the institute's boat Bay Eagle Monday as a four-legged platform was lowered into the York River.

Attached to the platform are various sensors and instruments that measure the movement of sediment and currents along the bottom of the river. For the next three weeks, until a crew from VIMS returns to pull it up, the platform will take regular vital signs of the river bottom.

The project is part of a three-year, $1 million study paid for by the Navy. Because toxic pollutants often get trapped in the muddy bottoms of bays and rivers, the Navy wants to know where sediments move and why, to help it keep track of its own messes. As the sediment goes, so goes the pollution.

Currents, storms and sedimentation rates - the rate silt filters down from the water - go a long way in explaining how mud moves around the bottom. But they doesn't tell the whole story.

That's where the worms come in.

Animals move mud around. Burrowing blue crabs kick it up, for example, and digging worms pull it down. At a normal sedimentation rate, a spot of pollution would be covered with a half inch of silt after about a year, Schaffner said.

``An organism can take that same material and move it down 5 or 10 inches in a week,'' she said.

One of the most influential organisms on the bottoms of rivers and bays are worms, if only by virtue of sheer numbers. Of the 4,000 tiny animals you'd expect to find in a square yard of river bottom, half or more would be worms, Schaffner said.

Schaffner used an X-ray of a cross section of bay bottom to illustrate the effect animals can have on sediment. In some parts of the X-ray, sediment was layered evenly, like the rings on a tree, while in other parts the layers disappeared in swirls and dips where crabs, worms and other creatures disturbed it.

``This sediment is like a historical record for us,'' Schaffner said.

The platform, on the other hand, will help Wright and Schaffner predict the future.

It was lowered into about 25 feet of water near Ferry Point, about 12 miles up river from the Coleman Bridge. It's far from the Navy's busiest harbors in Norfolk and Portsmouth, but the results from the York should show how things work in other rivers, including the Elizabeth.

``If we can look at soft bottoms up here, we can get an idea of how soft bottoms are going to behave down there,'' Wright said.

By soft bottoms, Wright means mud. The patch of the York where the platform was lowered Monday is so soft that you could push your arm into it up to your shoulder, he said. The platform's four big, flat feet kept it from sinking more than an inch down.

Measurements from the instruments, combined with sediment samples from the river bottom, will give Schaffner and Wright some idea how animals and their surroundings combine to move sediment around. A crab may kick up the mud, but the current and other factors will decide where it settles again.

Monday was the third time Wright and Schaffner have lowered the platform onto this spot in the river this year. They'll do it again in October, then report their findings for the year to the Navy by Christmas. They have already provided similar reports from areas in the lower end of Chesapeake Bay.

What the Navy will do with the information is anyone's guess at this point, Wright said.

``I'm sure it will be used,'' he said. ``But it may be a decade before the research is passed down to the Navy's operating practices.''